There seems to have been a recent change in Discourse with One Box url encoding.
I run a website that generates links like: www.discourse.org/?a=a%2Cb where %2C is the encoded version of the comma. If I paste this link to a one box:
The generated link is:
The encoded comma became %252C.
If you run encodeURIComponent(encodeURIComponent(',')) the result is %252C. IMHO the correct behavior would be not to encode already encoded characters. For example the ampersand works correctly with the latest discourse (Onebox incorrectly encodes urls with ampersands).